1. Field of the Invention
The present invention relates to an improved rail cushion assembly for use as a supporting cushion between a railroad rail and a railroad tie, especially a concrete railroad tie. More particularly, the present invention relates to an improved rail cushion assembly that includes a resilient rail pad that is in contact with the bottom flange surface of the railroad rail, and an abrasion-resistant plate that is positioned between the rail pad and a concrete railroad tie. The abrasion-resistant plate serves to minimize abrasion by sand and debris of the upper surface of the concrete railroad tie and of the lower surface of the rail pad as a result of movement of trains along the rail, thereby lengthening the useful operating life of the rail pad assembly.
2. Description of the Related Art
Anti-abrasion arrangements of various configurations have been proposed in the past for minimizing abrasion of the surfaces of concrete railroad ties and of the resilient pads that are placed between the railroad tie and the steel rail. It has been shown that two-part assemblies, consisting of a resilient pad positioned on an abrasion-resistant lower plate, have offered some relief to the problem of concrete tie abrasion at positions directly beneath the rails. One example of such a two-part system is illustrated and described in U.S. Pat. No. 5,405,081, entitled “Anti-Abrasion Rail Seat System,” which issued on Apr. 11, 1995 to, John H. Bosshart.
The function of the abrasion plate in a two-part anti-abrasion system is to provide an abrasion-resistant, bearing-type surface between the resilient rail pad and the concrete tie surface. The resilient pad can then flex and shift along the surface of the abrasion plate, rather than flex and shift along the concrete tie surface, when it is subjected to the heavy and varying compressive loads that are imposed upon the rail pads by the weight of moving trains. Such heavy and varying compressive loading causes the resilient pad to be cyclically partially compressed vertically. And as a result of the vertical pressures applied to the pad, it is also spread or extended horizontally. Such horizontal spread of the pad material results in relative lateral movement between the resilient pad and the surface that it rests against. Without the presence of an intervening abrasion plate, the horizontal spreading of the pad, combined with the sand, grit, and debris generally present in such environments, provides the pad surface movement and resulting abrading action that causes the abrasion of the upper surface of the concrete tie, as well as of the abutting rail pad surface. As a result, the effective operating life of the rail pad and of the concrete tie is significantly reduced.
The presence of an abrasion plate that is positioned between the resilient rail pad and the concrete tie serves to prevent that periodic abrading action from taking place between the resilient rail pad lower surface and the upper surface of the concrete tie. Any relative rail pad movement or spreading resulting from pad flexing, or from any other applied load, is intended to take place between the resilient pad surface and the abrasion plate surface, and not between the resilient pad surface and the upper surface of the concrete tie. Testing has shown that concrete tie abrasion can be significantly diminished by positioning a highly wear resistant surface between the resilient rail pad and the upper surface of the concrete tie.
Experience has shown, however, that the same desirable bearing and abrasion resistance properties of currently utilized abrasion plate materials can also cause the abrasion plate to slide out from between the resilient rail pad and the tie, either longitudinally or laterally, when the combination is subjected to the cyclically-varying compressive loading described above. Thus, there is a need for improved resilient rail pad and abrasion plate designs and assemblies that permit the two components to be separately produced as physically independent parts, yet be effectively interconnected in such a way that the two components continue to work together as a system and to remain properly positioned on the tie, as well as relative to each other.
One proposal for an interconnected resilient rail pad and abrasion plate is disclosed in published patent application No. US 2004/0113133 A1, entitled “Abrasion Assembly for Supporting Railroad Ties,” which was published on Jun. 17, 2004, and which names William Hugo Geissele et al. as inventors. That publication discloses a rail pad that includes a number of surface depressions formed on its lower surface, and an injection molded, thermoplastic polymer abrasion plate that includes a number of correspondingly-positioned surface protrusions that are formed on its upper, rail-pad-facing surface. The depressions and protrusions interengage with each other when the resilient pad and the abrasion plate are placed in face-to-face contact with each other, so that the protrusions are received in the depressions, to prevent substantial relative sliding movement and lateral separation between the rail pad and the abrasion plate.
Additionally, as a further interconnection arrangement, the structure disclosed by Geissele et al. includes a resilient rail pad having a hole at each of the four corners. The rail pad holes receive correspondingly-positioned, upstanding, molded stalks or pins that are carried at the corners of the molded thermoplastic abrasion plate and that extend through the rail pad holes when the pad and plate are placed together. The tips of the stalks or pins are deformed by the application of heat to cause the tips to mushroom and thereby non-removably retain the pad and plate together. The result is a two-part, interconnected and interengaged pad and plate assembly that serves to limit relative movement of the pad and plate, but that also provides the constraints to limit excessive and problematic pad and plate separation that could lead to tie surface contact of the pad and possible pad abrasion and tie abrasion.
The interconnection arrangement disclosed in the above-identified Geissele et al. published application requires the use of an injection-moldable grade of polymeric material to provide the necessary protrusions and pins of the disclosed abrasion plate design. Consequently, the use of high performance, non-injection-moldable grades of materials is necessarily excluded. For example, if ultra high molecular weight polyethylene (UHMWPE) were to be desired to be utilized as the abrasion plate material in the Geissele et al. arrangement, it would be disqualified because that material cannot be injection molded. That and other highly abrasion resistant, ultra high molecular weight materials typically exhibit zero melt flow when heated above their melt temperature, and therefore they can only be manufactured in flat profiles using high-pressure compression-molding processes. Complex, three-dimensional profiles of UHMW materials can only be achieved through costly, post-molding machining of thick sheets to provide the disclosed surface features, and thus such raw material options are economically foreclosed from consideration in designs such as the one proposed by Geissele et al. In addition to UHMW polyethylene, other high performance UHMW polymers (e.g., UHMW acetal or UHMW nylon) having superior abrasion-resistant performance properties would also be eliminated from consideration in the Geissele et al. arrangement.
Therefore, in order to utilize such superior, high-performance, longer-lasting materials as candidates in the manufacture of two-part rail pad assemblies, there is a need for a railroad pad assembly design that allows the use of a flat, two-dimensional abrasion plate. Such an assembly should also provide suitable constraints to keep the abrasion plate from shifting relative to the resilient pad by slipping out laterally when the assembly is exposed to the cyclic compressive loading normally encountered in a rail pad application. The present invention responds to that need.